The correct spelling is "practice". However, in many parts of the English speaking world (UK, Ireland, Australia, Canada, and South Africa) “practice” is the noun, “practise” the verb. So:- if you follow US convention, you don't need to worry about this as you can use practice for both noun and verb;- if you follow UK convention and you're not sure how to spot nouns and verbs, there are tricks you can use to help you (examples: "You need more practice", "You should practise more").